OOP in Python, specially Composition

2020-11-25 07:14 Paris imported from Stackoverflow

So, I've been trying to get my hands-on experience on Python and this OOP concept just started coming along. I can't seem to understand the concept of Composition clearly with good examples like a car example. Any help on this would be great!

I'll provide a code which uses Composition, Can anyone explain the use of Composition here?

class Clothing:
    stock={ 'name': [],'material' :[], 'amount':[]}
  def __init__(self, name):
      material = ""
      self.name = name

  def add_item(self, name, material, amount):
      Clothing.stock['name'].append(self.name)
      Clothing.stock['material'].append(self.material)
      Clothing.stock['amount'].append(amount)

  def Stock_by_Material(self, material):
      count=0
      n=0
      for item in Clothing.stock['material']:
          if item == material:
              count += Clothing.stock['amount'][n]
              n+=1
      return count

  class shirt(Clothing):
      material="Cotton"

  class pants(Clothing):
      material="Cotton"

  polo = shirt("Polo")
  sweatpants = pants("Sweatpants")

  polo.add_item(polo.name, polo.material, 4)
  sweatpants.add_item(sweatpants.name, sweatpants.material, 6)

  current_stock = polo.Stock_by_Material("Cotton")
  print(current_stock)

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```
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```
from sympy import Ynm
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Image not showing properly when reading the image using PIL instead of imagio library

I have this code that converts an image from RGB space to HSI space:

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plt.imshow(hsi_cat)
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This results is a black image, and I'm not quite sure why!

Maintaining global but changeable variables across classes/packages

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how to stop form submitting if form is invalid in vue3 cli compostion apis in vee validate

i am new to vue3 and composition apis. there is problem with validating a simple form. i am trying to stop form submission if form is not valid or not touched as it is vaild by default if inputs not touched.

<form @submit="onSubmit">
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  </div>
  <div class="login-buttons">
    <button
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    </button>
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</form>

<script>
import { useForm, useField,useIsFormValid } from "vee-validate";
import * as yup from "yup";

export default {
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      validate,
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    // Define a validation schema
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    const onSubmit = handleSubmit(async () => {
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        return;
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      emailError,
      password,
      passwordError,
      onSubmit
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};
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in handelSubmit function if (vaild.value === false) it should return and stop the logic but always the value for vaild is true so it continues the HTTP calling for the api.

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Best practice to avoid duplication of methods in two classes using a list of objects of another class?

This a bit like the inheritance and composition discussion but here we have a list of objects. The problem: I have two classes GuidedTour and TourGuide both having a list of DateRange objects. I want to avoid duplicating methods operating on the DateRange objects like add_date_ranges, get_date_ranges, count_date_ranges, etc.

class DateRange:

    def __init__(self, date_from, date_last):
        self.date_from = date_from
        self.date_last = date_last

class GuidedTour:

    def __init__(self):
        self.date_ranges = []

    def add_date_range(self, date_from, date_last):
        self.date_ranges.append(DateRange(date_from, date_last))

class TourGuide:

    def __init__(self):
        self.date_ranges = []

    def add_date_range(self, date_from, date_last):
        self.date_ranges.append(DateRange(date_from, date_last))

Two ways to solve this.

Inheritance. Create a class TourDateRanges inherited by both the GuidedTour and TourGuide classes with all methods operating on the DateRange objects.

class DateRange:

    def __init__(self, date_from, date_last):
        self.date_from = date_from
        self.date_last = date_last

class TourDateRanges:
    
    def add_date_range(self, date_from, date_last):
        self.date_ranges.append(DateRange(date_from, date_last))

class GuidedTour(TourDateRanges):

    def __init__(self):
        self.date_ranges = []

class TourGuide(TourDateRanges):

    def __init__(self):
        self.date_ranges = []

Now I can do:

date_from = '2021-08-01'
date_last = '2021-08-31'
guided_tour = GuidedTour()
guided_tour.add_date_range(date_from, date_last)

Composition. Create a class TourDateRange as above but this time this class is added to the GuidedTour and TourGuide classes.

class DateRange:

    def __init__(self, date_from, date_last):
        self.date_from = date_from
        self.date_last = date_last

class TourDateRanges:
    
    def __init__(self):
        self.date_ranges = []

    def add_date_range(self, date_from, date_last):
        self.date_ranges.append(DateRange(date_from, date_last))

class GuidedTour:

    def __init__(self):
        self.tour_date_ranges = TourDateRanges()

class TourGuide:

    def __init__(self):
        self.tour_date_ranges = TourDateRanges()

Now I can do:

date_from = '2021-08-01'
date_last = '2021-08-31'
guided_tour = GuidedTour()
guided_tour.tour_date_ranges.add_date_range(date_from, date_last)

I prefer the composition option, but I'm not sure I'm right and maybe there are other ways to solve this.

Is there any way to call constructor of child class using object of parent class in JAVA?

I have a problem in composition in Java. I want to access the constructor of a class located inside another class. Now if I made an object of parent class and want to access constructor of child class. Is there any possible way to do it?

Here's the code of the both classes and runner class.

package compositon.student;
public class phone {
    String countryCode;
    String number;
    public phone(){}//empty constructor
    public phone(String countryCode, String number)
    {
        this.countryCode = countryCode;
        this.number = number;
    }
}

package compositon.student;

public class address {
    String Street_address;
    String town;
    String city;
    String country;
    
    phone number  = new phone(); //object from class phone, by using composition of classes
    
    public static void main(String[] args) {
        address objAddress = new address();
        objAddress.number()
    }
}

What is the correct way to access a class composite inside one of its components, if that's even advisable?
Suppose I have these two classes:
```
class Branch():
    def __init__(self, id, leaves):
        self.id = id
        self.leaves = leaves
    
class Leaf():
    def __init__(self, color)
        self.color = color
    
    def describe()
        print("This leaf is " + color)
```
Every Leaf belongs to a Branch. A Branch continues to exist whether it has any leaves or not, but a Leaf cannot meaningfully exist without a Branch (real-life logic aside). That means I can easily get every Leaf from a Branch through the Branch.leaves attribute. If I understood composition correctly, a Branch is the composite and every Leaf in Branch.leaves is one of its components?

However, no Leaf actually knows to which Branch it belongs to. So, I can't have it print "This leaf is orange and belongs to branch #14". I could just add a Leaf.branch attribute and pass it whenever I initialize a new Leaf instance, seeing how a Branch must already exist for that to happen, but that seems very wrong to me, because then it looks like the Branch belongs to the Leaf.

The question is: what is the most pythonic and correct way to do what I described I can't do in my example? Is what I thought felt very wrong not actually bad at all? Or rather, did this problem arise from bad design and I should look at this from another angle? Thanks in advance.

Providing an example of composition for these classes

Trying to learn more about concepts in C#. Would anyone be able to explain how composition could be used between these two classes:

class Book
    {
        string Title;
        string Author;
        string Year;

        public Book(string Title, string Author, string Year)
        {
            this.Title = Title;
            this.Author = Author;
            this.Year = Year;
        }

        public void Display()
        {
            Console.WriteLine(Title + " " + Author);
        }
    }

    class BookTest
    {
        public static void Main(string[] args)
        {
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LNK2019 Unresolved external symbol while composing two classes into one

I have created two classes Name and Date to use it in another class LibraryBook, but the code gives me an unresolved external symbol. I am compiling this code in Visual Studio 2019.

The name class stores a first name and a last name. The date class stores date in DD-MM-YYYY format. The Library book class has following attributes:

char* const ISBN;     // stores the ISBN of the book
char* title;          // stores the title of the book
const Name author;    // stores the name of author
Name publisher;       // stores the name of publisher
int quantity;         // stores the quantitiy of book
Date lastIssue;       // stores the latest issue date of the book.

The unresolved externals I am getting are:

1>LibraryBook.obj : error LNK2019: unresolved external symbol "public: __thiscall Date::Date(class Date const &)" (??0Date@@QAE@ABV0@@Z) referenced in function "public: __thiscall LibraryBook::LibraryBook(char * const,char *,class Name,class Name,class Date,int)" (??0LibraryBook@@QAE@QADPADVName@@2VDate@@H@Z)
1>LibraryBook.obj : error LNK2019: unresolved external symbol "public: void __thiscall Date::showDate(void)const " (?showDate@Date@@QBEXXZ) referenced in function "public: void __thiscall LibraryBook::displayBookDetails(void)" (?displayBookDetails@LibraryBook@@QAEXXZ)
1>LibraryBook.obj : error LNK2019: unresolved external symbol "public: __thiscall Date::~Date(void)" (??1Date@@QAE@XZ) referenced in function "public: __thiscall LibraryBook::LibraryBook(char * const,char *,class Name,class Name,class Date,int)" (??0LibraryBook@@QAE@QADPADVName@@2VDate@@H@Z)
1>LibraryBook.obj : error LNK2019: unresolved external symbol "public: __thiscall Name::Name(class Name const &)" (??0Name@@QAE@ABV0@@Z) referenced in function "public: __thiscall LibraryBook::LibraryBook(char * const,char *,class Name,class Name,class Date,int)" (??0LibraryBook@@QAE@QADPADVName@@2VDate@@H@Z)
1>LibraryBook.obj : error LNK2019: unresolved external symbol "public: __thiscall Name::~Name(void)" (??1Name@@QAE@XZ) referenced in function "public: __thiscall LibraryBook::LibraryBook(char * const,char *,class Name,class Name,class Date,int)" (??0LibraryBook@@QAE@QADPADVName@@2VDate@@H@Z)
1>LibraryBook.obj : error LNK2019: unresolved external symbol "public: char * __thiscall Name::fullName(void)" (?fullName@Name@@QAEPADXZ) referenced in function "public: void __thiscall LibraryBook::displayBookDetails(void)" (?displayBookDetails@LibraryBook@@QAEXXZ)

Name.h

#pragma once
#include<iostream>
using namespace std;
class Name
{
public:
    Name(char* = nullptr, char* = nullptr); //parametrized constructor with default arguments
    Name(const Name&);  //  copy constructor
    ~Name();    //  destructor (should release all dynamic allocations)
    
    void copyName(Name&);   //this is not a copy constructor, I want this function to copy the contents of
                            //one name(firstName and lastName both) to another name.
                                    //  Function copies the contents of the calling object to the passing object. i.e...
                                //  ...name.firstNamee = this->firstName and name.lastName = this->lastName

                    //  The function will copy the contents of the calling object to the passing object.
    void camelCase();   //  make first letter capital of both attributes
    void toLower(); //  convert name to lower case alphabets
    void toUpper(); //  convert name to upper case alphabets
    int nameLength();   //  both first and last excluding space.    Try for this name: Mohammad Hassan Zubair
    void swapName();    //  firstName becomes lastName and vice versa
    void display(); //  prints name(firstName and lastName with space in between)
    char* fullName();   //  concatenate both attributes and return full name with a space in between both
    //  provide setters/getters for Name class. Remember: setters with no memory leakage.
    //  provide other relevant methods you want like your own strLength and strCopy function etc.
    //  provide relevant methods for const objects too.

    void setFirstName(char* firstName); //  no memory leakage
    char* getFirstName() const; //  no memory leakage
    void setLastName(char* lastName);   //  no memory leakage
    char* getLastName() const;  //  no memory leakage

    //for const objects

    //void copyName(const Name&) const; //  this method is not valid as a const object cannot be modified.
    void copyName(Name&) const; //this is not a copy constructor, I want this function to copy the contents of
                                    //one name(firstName and lastName both) to another name.
                                //  Function copies the contents of the calling object to the passing object. i.e...
                                //  ...name.firstNamee = this->firstName and name.lastName = this->lastName

    void camelCase() const; //  make first letter capital of both attributes
    void toLower() const;   //  convert name to lower case alphabets
    void toUpper() const;   //  convert name to upper case alphabets
    int nameLength() const; //  both first and last excluding space.
    //void swapName() const;    //  cannot modify attributes of a const function so no swapName for this function
    void display() const;   //  prints name(firstName and lastName with space in between)
    char* fullName() const; //  concatenate both attributes and return full name with a space in between both

    //  No setters and getters for a const object as it is const.

private:
    char* firstName;
    char* lastName;
    bool isValidName(); //  name should contain only alphabets - no special characters or digits
    int strLen(char*);  //  calculates the length of a string
    char* deepCopyArr(char* arr);

    int strLen(char*) const;    //  calculates the length of a string
    char* deepCopyArr(char* arr) const;
};

Name.cpp

#include "Name.h"

Name::Name(char* firstName, char* lastName) //parametrized constructor with default arguments
{
    //firstName is neccessary for lastName.
    if (firstName)
    {
        this->firstName = deepCopyArr(firstName);
        if (lastName)
        {
            this->lastName = deepCopyArr(lastName);
        }
        else this->lastName = lastName;
        if (!isValidName()) //if name is invalid, nullptr is assigned to the name.
        {
            delete[] this->firstName;
            this->firstName = nullptr;
            delete[] this->lastName;
            this->lastName = nullptr;
        }
    }
    else
    {
        this->firstName = nullptr;
        this->lastName = nullptr;
    }

}
Name::Name(const Name& name)    //  copy constructor
{
    //No need to check validation of name here as its callin object(name) cannot have an invalid name.
    //The calling object must have a valid name as it would have gone through the name-validation process in its constructor.
    if (name.firstName)
    {
        this->firstName = deepCopyArr(name.firstName);
        if (name.lastName)
        {
            this->lastName = deepCopyArr(name.lastName);
        }
        else this->lastName = name.lastName;
    }
    else
    {
        this->firstName = name.firstName;
        this->lastName = name.lastName;
    }
}
Name::~Name()
{
    if (this->firstName)
    {
        delete[] this->firstName;
        this->firstName = nullptr;
    }
    if (this->lastName)
    {
        delete[] this->lastName;
        this->lastName = nullptr;
    }
}

void Name::copyName(Name& name) 
{
    //  Function copies the contents of the calling object to the passing object. i.e...
    //  ...name.firstNamee = this->firstName and name.lastName = this->lastName


    if (name.firstName)
    {
        delete[] name.firstName;
        name.firstName = nullptr;
        if (name.lastName)
        {
            delete[] name.lastName;
            name.lastName = nullptr;
        }
    }
    if (this->firstName)
    {
        name.firstName = deepCopyArr(this->firstName);
        if (this->lastName)
        {
            name.lastName = deepCopyArr(this->lastName);
        }
        else
            name.lastName = nullptr;
    }
    else
    {
        name.firstName = nullptr;
        name.lastName = nullptr;
    }
}
void Name::camelCase()  //  make first letter capital of both attributes
{
    if (firstName)
    {
        int len_01 = strLen(firstName);
        //convert firstName to camel case here.
        if (firstName[0] >= 97 && firstName[0] <= 123)
        {
            firstName[0] -= 32;
        }
        for (int i = 1; i < len_01; i++)
        {
            if (firstName[i] >= 65 && firstName[i] <= 91)
            {
                firstName[i] += 32;
            }
        }

        if (lastName)   //convert lastName to camelCase here.
        {
            int len_02 = strLen(lastName);
            if (lastName[0] >= 97 && lastName[0] <= 123)
            {
                lastName[0] -= 32;
            }
            for (int i = 1; i < len_01; i++)
            {
                if (lastName[i] >= 65 && lastName[i] <= 91)
                {
                    lastName[i] += 32;
                }
            }
        }
    }
}
void Name::toLower()    //  convert name to lower case alphabets
{
    if (this->firstName)
    {
        for (int i = 0; i < strLen(this->firstName); i++)
        {
            if (this->firstName[i] >= 65 && this->firstName[i] <= 91)
                this->firstName[i] += 32;
        }

        if (this->lastName)
        {
            for (int i = 0; i < strLen(this->lastName); i++)
            {
                if (this->lastName[i] >= 65 && this->lastName[i] <= 91)
                    this->lastName[i] += 32;
            }
        }
    }
}
void Name::toUpper()    //  convert name to upper case alphabets
{
    if (this->firstName)
    {
        for (int i = 0; i < strLen(this->firstName); i++)
        {
            if (this->firstName[i] >= 97 && this->firstName[i] <= 123)
                this->firstName[i] -= 32;
        }

        if (this->lastName)
        {
            for (int i = 0; i < strLen(this->lastName); i++)
            {
                if (this->lastName[i] >= 97 && this->lastName[i] <= 123)
                    this->lastName[i] -= 32;
            }
        }
    }
}
int Name::nameLength()  //  both first and last excluding space.    Try for this name: Mohammad Hassan Zubair
{
    if (this->firstName && this->lastName)
    {
        return strLen(this->firstName) + strLen(this->lastName);
    }
    else if (this->firstName)
    {
        return strLen(this->firstName);
    }
    else return 0;
}
void Name::swapName()   //  firstName becomes lastName and vice versa
{
    if (this->firstName && this->lastName)
    {
        char* temp_fN = deepCopyArr(this->lastName);
        char* temp_lN = deepCopyArr(this->firstName);

        delete[] this->firstName;
        this->firstName = temp_fN;

        delete[] this->lastName;
        this->lastName = temp_lN;
    }
}
void Name::display()
{
    if (this->firstName)
    {
        cout << this->firstName;
        if (this->lastName)
        {
            cout << ' ' << this->lastName;
        }
    }
}
char* Name::fullName()  //  concatenate both attributes and return full name with a space in between both
{
    if (this->firstName && this->lastName)
    {
        int length = strLen(this->firstName) + 1 + strLen(this->lastName);
        //  I have used strLen() function various times instead of storing its result in a variable to avoid...
        //...buffer overrun.

        char* fullName = new char[length + 1]{ 0 };
        for (int i = 0; i < strLen(this->firstName); i++)
        {
            fullName[i] = this->firstName[i];
        }

        fullName[strLen(this->firstName)] = ' ';

        for (int i = 0; i < strLen(this->lastName); i++)
        {
            fullName[i + strLen(this->firstName) + 1] = this->lastName[i];
        }
        return fullName;
    }
    else if (this->firstName)
    {
        return deepCopyArr(this->firstName);
    }
    else
    {
        return nullptr;
    }
}

int Name::strLen(char* arr) //  calculates the length of a string
{
    int length = 0;
    for (; arr[length] != '\0'; length++);
    return length;
}
bool Name::isValidName()    //  name should contain only alphabets - no special characters or digits
{
    if (this->firstName)
    {
        for (int i = 0; i < strLen(this->firstName); i++)
        {
            if (this->firstName[i] < 65 || this->firstName[i] > 91 && this->firstName[i] < 97 || this->firstName[i] > 123)
                return false;
        }
        if (this->lastName)
        {
            for (int i = 0; i < strLen(lastName); i++)
            {
                if (this->lastName[i] < 65 || this->lastName[i] > 91 && this->lastName[i] < 97 || this->lastName[i] > 123)
                    return false;
            }
        }
    }
    return true;
}
char* Name::deepCopyArr(char* arr)  //returns an arr to copy.
{
    int length = strLen(arr);
    char* new_arr = new char[length + 1]{ '\0' };
    for (int i = 0; i < length; i++)
    {
        new_arr[i] = arr[i];
    }
    new_arr[length] = '\0';
    return new_arr;
}

void Name::setFirstName(char* firstName)
{
    this->firstName = deepCopyArr(firstName);
    if (!isValidName())
    {
        delete[] this->firstName;
        this->firstName = nullptr;
    }
}
char* Name::getFirstName() const
{
    if (this->firstName)
        return deepCopyArr(this->firstName);
    else
        return nullptr;
}
void Name::setLastName(char* lastName)
{
    if (this->firstName)
    {
        this->lastName = deepCopyArr(lastName);
        if (!isValidName())
        {
            delete[] this->lastName;
            this->lastName = nullptr;
        }
    }
    else this->lastName = nullptr;
}
char* Name::getLastName() const
{
    if (this->lastName)
        return deepCopyArr(lastName);
    else
        return nullptr;
}

//  For const objects

int Name::strLen(char* arr) const   //  calculates the length of a string
{
    int length = 0;
    for (; arr[length] != '\0'; length++);
    return length;
}
char* Name::deepCopyArr(char* arr) const    //returns an arr to copy.
{
    int length = 0;
    for (; arr[length] != '\0'; length++);

    char* new_arr = new char[length + 1]{ '\0' };
    for (int i = 0; i < length; i++)
    {
        new_arr[i] = arr[i];
    }
    new_arr[length] = '\0';
    return new_arr;
}

void Name::camelCase() const    //  make first letter capital of both attributes
{
    if (firstName)
    {
        int len_01 = strLen(firstName);
        if (firstName[0] >= 97 && firstName[0] <= 123)
        {
            firstName[0] -= 32;
        }
        for (int i = 1; i < len_01; i++)
        {
            if (firstName[i] >= 65 && firstName[i] <= 91)
            {
                firstName[i] += 32;
            }
        }

        if (lastName)
        {
            int len_02 = strLen(lastName);
            if (lastName[0] >= 97 && lastName[0] <= 123)
            {
                lastName[0] -= 32;
            }
            for (int i = 1; i < len_01; i++)
            {
                if (lastName[i] >= 65 && lastName[i] <= 91)
                {
                    lastName[i] += 32;
                }
            }
        }

    }
}
void Name::toLower() const  //  convert name to lower case alphabets
{
    if (this->firstName)
    {
        for (int i = 0; i < strLen(this->firstName); i++)
        {
            if (this->firstName[i] >= 65 && this->firstName[i] <= 91)
                this->firstName[i] += 32;
        }

        if (this->lastName)
        {
            for (int i = 0; i < strLen(this->lastName); i++)
            {
                if (this->lastName[i] >= 65 && this->lastName[i] <= 91)
                    this->lastName[i] += 32;
            }
        }
    }
}
void Name::toUpper() const  //  convert name to upper case alphabets
{
    if (this->firstName)
    {
        for (int i = 0; i < strLen(this->firstName); i++)
        {
            if (this->firstName[i] >= 97 && this->firstName[i] <= 123)
                this->firstName[i] -= 32;
        }

        if (this->lastName)
        {
            for (int i = 0; i < strLen(this->lastName); i++)
            {
                if (this->lastName[i] >= 97 && this->lastName[i] <= 123)
                    this->lastName[i] -= 32;
            }
        }
    }
}
int Name::nameLength() const
{
    if (this->firstName)
    {
        int length = 0;
        for (int i = 0; i < strLen(this->firstName); i++)
        {
            if (this->firstName[i] != 32)
            {
                length++;
            }
        }
        if (this->lastName)
        {
            for (int i = 0; i < strLen(this->lastName); i++)
            {
                if (this->lastName[i] != 32)
                {
                    length++;
                }
            }
        }
        return length;
    }
    return 0;
}
void Name::display() const  //  prints name(firstName and lastName with space in between)
{
    if (this->firstName)
    {
        cout << this->firstName;
        if (this->lastName)
        {
            cout << ' ' << this->lastName;
        }
    }
}
char* Name::fullName() const    //  concatenate both attributes and return full name with a space in between both
{
    if (this->firstName && this->lastName)
    {
        int length = strLen(this->firstName) + 1 + strLen(this->lastName);
        //  I have used strLen() function various times instead of storing its result in a variable to avoid...
        //...buffer overrun.

        char* fullName = new char[length + 1]{ 0 };
        for (int i = 0; i < strLen(this->firstName); i++)
        {
            fullName[i] = this->firstName[i];
        }

        fullName[strLen(this->firstName)] = ' ';

        for (int i = 0; i < strLen(this->lastName); i++)
        {
            fullName[i + strLen(this->firstName) + 1] = this->lastName[i];
        }
        return fullName;
    }
    else if (this->firstName)
    {
        return deepCopyArr(this->firstName);
    }
    else
    {
        return nullptr;
    }
}
void Name::copyName(Name& name) const
{
    //  Function copies the contents of the calling object to the passing object. i.e...
    //  ...name.firstNamee = this->firstName and name.lastName = this->lastName
    if (name.firstName)
    {
        delete[] name.firstName;
        name.firstName = nullptr;
        if (name.lastName)
        {
            delete[] name.lastName;
            name.lastName = nullptr;
        }
    }
    if (this->firstName)
    {
        name.firstName = deepCopyArr(this->firstName);
        if (this->lastName)
        {
            name.lastName = deepCopyArr(this->lastName);
        }
        else
            name.lastName = nullptr;
    }
    else
    {
        name.firstName = nullptr;
        name.lastName = nullptr;
    }

}

Date.h

    #pragma once
    class Date
    {
    public:
        Date(); // initialize attributes with default values (01-01-2000)
        Date(int, int, int);    // if invalid, set members equal to default values (01-01-2000)
        Date(const Date&);      // A regular copy constructor
        bool inputDate();       // assign values to date attributes (cin from user),
                                    // return true if valid range of values are input else false
        bool copyDate(const Date&); // will behave similar to copy constructor
        bool inputCompleteDate(int, int, int);  // will behave similar to parameterized constructor
        const Date& getDate() const;
        void retrieveDate(int&, int&, int&) const;  // retrieve date attribute values using "pass by reference"
        void showDate() const;  // Display date attribute values on Console
        bool isEqual(Date&) const;  // return true if calling & passing date objects are equal  *THIS POINTER*
        bool isLeapYear() const;
        ~Date();        // A regular destructor
        
        void setDay(int _day);
        int getDay();
        void setMonth(int _month);
        int getMonth();
        void setYear(int _year);
        int getYear();
    
    private:
        bool validateDate() const;      //const it.
        int day;
        int month;
        int year;
    };

Date.cpp

#include "Date.h"
#include<iostream>
using namespace std;

Date::Date()    // initialize attributes with default values (01-01-2000)
{
    this->day = 01;
    this->month = 01;
    this->year = 01;
}
Date::Date(int day, int month, int year)    // if invalid, set members equal to default values (01-01-2000)
{
    this->day = day;
    this->month = month;
    this->year = year;
    if (!validateDate())
    {
        this->day = 1;
        this->month = 1;
        this->year = 2000;
    }
}
Date::Date(const Date& date)        // A regular copy constructor
{
    //No need to check validation of date here as the object that calls the copy constructor will have a valid date.
    this->day = date.day;
    this->month = date.month;
    this->year = date.year;
}
bool Date::inputDate()      // assign values to date attributes (cin from user),
{
    cout << "Enter day: ";
    cin >> this->day;
    cout << "Enter month: ";
    cin >> this->month;
    cout << "Enter year: ";
    cin >> this->year;

    if (!validateDate())
    {
        this->day = 1;
        this->month = 1;
        this->year = 2000;
        return false;
    }
    return true;
}
bool Date::copyDate(const Date& date)   // will behave similar to copy constructor
{
    //This function will always return true as its calling object(date) cannot have an invalid date.
    //The calling object must have a valid date as it would have gone through the date-validation process in its constructor.
    if (validateDate())
    {
        this->day = date.day;
        this->month = date.month;
        this->year = date.year;
        return true;
    }
    else    //This piece of code will never be exectued due to the reason I've stated above.
    {
        this->day = 1;
        this->month = 1;
        this->year = 2000;
        return false;
    }
}
bool Date::inputCompleteDate(int day, int month, int year)  // will behave similar to parameterized constructor
{
    this->day = day;
    this->month = month;
    this->year = year;
    if (!validateDate())
    {
        this->day = 1;
        this->month = 1;
        this->year = 2000;
        return false;
    }
    return true;
}
void Date::retrieveDate(int& _day, int& _month, int& _year) const   // retrieve date attribute values using "pass by reference"
{
    _day = this->day;
    _month = this->month;
    _year = this->year;
}
void Date::showDate() const // Display date attribute values on Console
{
    if (this->day < 10)
    {
        cout << '0';
    }
    cout << this->day << '-';

    if (this->month < 10)
    {
        cout << '0';
    }   
    cout << this->month << '-';
    
    if (this->year < 10)
    {
        cout << "000";
    }
    else if (this->year < 100 && this->year >= 10)
    {
        cout << "00";
    }
    else if (this->year < 1000 && this->year >= 100)
    {
        cout << '0';
    }
    cout << this->year;
}
bool Date::isEqual(Date& date) const    // return true if calling & passing date objects are equal  *THIS POINTER*
{
    if (this->day == date.day && this->month == date.month && this->year == date.year) return true;
    return false;
}
bool Date::isLeapYear() const
{
    if (year % 4 == 0)
    {
        if (year % 100 == 0)
        {
            if (year % 400 == 0)
            {
                return true;
            }
            else
            {
                return false;
            }
        }
        else
            return true;
    }
    else
    {
        return false;
    }
}
Date::~Date()       // A regular destructor
{
    this->day = 0;
    this->month = 0;
    this->year = 0;
}
void Date::setDay(int _day)
{
    this->day = _day;
    if (!validateDate())
    {
        this->day = 1;
        this->month = 1;
        this->year = 2000;
    }
}
int Date::getDay()
{
    return this->day;
}
void Date::setMonth(int _month)
{
    this->month = _month;
    if (!validateDate())
    {
        this->day = 1;
        this->month = 1;
        this->year = 2000;
    }
}
int Date::getMonth()
{
    return this->month;
}
void Date::setYear(int _year)
{
    this->year = year;
    if (!validateDate())
    {
        this->day = 1;
        this->month = 1;
        this->year = 2000;
    }
}
int Date::getYear()
{
    return this->year;
}
bool Date::validateDate() const
{
    bool isMoreDays = 0;
    bool _isLeapYear = isLeapYear();

    if (month <= 7 && month % 2 != 0)
        isMoreDays = true;
    else if (month >= 8 && month % 2 == 0)
        isMoreDays = true;
    else isMoreDays = false;

    if (day <= 0)
        return false;
    if (day >= 32 && isMoreDays)
        return false;
    if (day >= 31 && !isMoreDays)
        return false;
    if (month == 2 && day >= 29 && !_isLeapYear)
        return false;
    if (month == 2 && day >= 30 && _isLeapYear)
        return false;
    if (month <= 0)
        return false;
    if (month >= 13)
        return false;
    if (year <= 0)
        return false;
    return true;
}

/////   Please read the following comment   /////
/*Date& Date::getDate() const
{
    There is no description provided in the function.
    Function will have no use as it is const and returning by reference at the same time.
    To make use of this function, consider the following code:  

    static Date temp;       //The object is static so that it won't be deleted when the scope of this function ends.
    temp.day = this->day;
    temp.month = this->month;
    temp.year = this->year;
    return temp;

    //Another way to make use of this code is by making it non-const or change it's return-type to const Date&.
}*/
/////   Please read the comment above   /////

const Date& Date::getDate() const
{
    return *this;
}

LibraryBook.h

#pragma once
#include"Date.h"
#include"Name.h"
#include<iostream>
using namespace std;

class LibraryBook
{
public:
    LibraryBook(char* const, char*, Name,  Name, Date, int);
    ~LibraryBook();
    void displayBookDetails();
private:
    char* const ISBN;
    char* title;
    Name publisher;
    Name author;
    Date lastIssue;
    int quantity;

    char* deepCopyArr(char* arr);
};

LibraryBook.cpp

#include "LibraryBook.h"

char* LibraryBook::deepCopyArr(char* arr)   //returns an arr to copy.
{
    int length{ 0 }; for (; arr[length] != '\0'; length++);
    char* new_arr = new char[length + 1]{ '\0' };
    for (int i = 0; i < length; i++)
    {
        new_arr[i] = arr[i];
    }
    new_arr[length] = '\0';
    return new_arr;
}

LibraryBook::LibraryBook(char* const _ISBN, char* _t, Name _p, Name _a, Date _lI, int _q)
    :ISBN(_ISBN),title(deepCopyArr(_t)),publisher(publisher = _p),author(author = _a),lastIssue(_lI),quantity(_q)
{
    //stitle = deepCopyArr(_t);
    //quantity = _q;
}

LibraryBook::~LibraryBook()
{
    // Destructor
}

void LibraryBook::displayBookDetails()
{
    cout << "ISBN: " << ISBN << '\n';
    cout << "Title: " << title << '\n';
    cout << "Author: " << author.fullName() << '\n';
    cout << "Publisher: " << publisher.fullName() << '\n';
    cout << "Quantitiy: " << quantity << '\n';
    cout << "Last Issue: "; lastIssue.showDate(); cout << '\n';
}

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